1. Field of the Invention
This invention relates generally to nucleic acid sequences encoding proteins that are associated with abiotic stress responses and abiotic stress tolerance in plants. In particular, this invention relates to nucleic acid sequences encoding proteins that confer drought, cold, and/or salt tolerance to plants.
2. Background Art
Abiotic environmental stresses, such as drought stress, salinity stress, heat stress, and cold stress, are major limiting factors of plant growth and productivity. Crop losses and crop yield losses of major crops such as rice, maize (corn) and wheat caused by these stresses represent a significant economic and political factor and contribute to food shortages in many underdeveloped countries.
Plants are typically exposed during their life cycle to conditions of reduced environmental water content. Most plants have evolved strategies to protect themselves against these conditions of desiccation. However, if the severity and duration of the drought conditions are too great, the effects on plant development, growth and yield of most crop plants are profound. Furthermore, most of the crop plants are very susceptible to higher salt concentrations in the soil. Continuous exposure to drought and high salt causes major alterations in the plant metabolism. These great changes in metabolism ultimately lead to cell death and consequently yield losses.
Developing stress-tolerant plants is a strategy that has the potential to solve or mediate at least some of these problems. However, traditional plant breeding strategies to develop new lines of plants that exhibit resistance (tolerance) to these types of stresses are relatively slow and require specific resistant lines for crossing with the desired line. Limited germplasm resources for stress tolerance and incompatibility in crosses between distantly related plant species represent significant problems encountered in conventional breeding. Additionally, the cellular processes leading to drought, cold and salt tolerance in model, drought- and/or salt-tolerant plants are complex in nature and involve multiple mechanisms of cellular adaptation and numerous metabolic pathways. This multi-component nature of stress tolerance has not only made breeding for tolerance largely unsuccessful, but has also limited the ability to genetically engineer stress tolerance plants using biotechnological methods.
Therefore, what is needed is the identification of the genes and proteins involved in these multi-component processes leading to stress tolerance. Elucidating the function of genes expressed in stress tolerant plants will not only advance our understanding of plant adaptation and tolerance to environmental stresses, but also may provide important information for designing new strategies for crop improvement.
One model plant used in the study of stress tolerance is Arabidopsis thaliana. There are at least four different signal-transduction pathways leading to stress tolerance in the model plant Arabidopsis thaliana. These pathways are under the control of distinct transcription factors (Shinozaki et al., 2000 Curr. Op. PI. Biol. 3:217-23). Regulators of genes, especially transcription factors, involved in these tolerance pathways are particularly suitable for engineering tolerance into plants because a single gene can activate a whole cascade of genes leading to the tolerant phenotype. Consequently, transcription factors are important targets in the quest to identify genes conferring stress tolerance to plants.
One transcription factor that has been identified in the prior art is the Arabidopsis thaliana transcription factor CBF (Jaglo-Ottosen et al., 1998 Science 280:104-6). Over-expression of this gene in Arabidopsis conferred drought tolerance to this plant (Kasuga et al., 1999 Nature Biotech. 17:287-91). However, CBF is the only example to date of a transcription factor able to confer drought tolerance to plants upon over-expression.
Although some genes that are involved in stress responses in plants have been characterized, the characterization and cloning of plant genes that confer stress tolerance remains largely incomplete and fragmented. For example, certain studies have indicated that drought and salt stress in some plants may be due to additive gene effects, in contrast to other research that indicates specific genes are transcriptionally activated in vegetative tissue of plants under osmotic stress conditions. Although it is generally assumed that stress-induced proteins have a role in tolerance, direct evidence is still lacking, and the functions of many stress-responsive genes are unknown.
There is a need, therefore, to identify genes expressed in stress tolerant plants that have the capacity to confer stress resistance to its host plant and to other plant species. Newly generated stress tolerant plants will have many advantages, such as increasing the range that crop plants can be cultivated by, for example, decreasing the water requirements of a plant species.
This invention fulfills in part the need to identify new, unique transcription factors capable of conferring stress tolerance to plants upon over-expression. The present invention provides a transgenic plant cell transformed by a Transcription Factor Stress-Related Protein (TFSRP) coding nucleic acid, wherein expression of the nucleic acid sequence in the plant cell results in increased tolerance to environmental stress as compared to a wild type variety of the plant cell. Namely, described herein are the transcription factors 1) CAAT-Box like Binding Factor-3 (CABF-3); 2) Zinc Finger-2 (ZF-2) 3) Zinc Finger-3 (ZF-3) Zinc Finger-4 (ZF-4); 5) Zinc Finger-5 (ZF-5); 6)AP2 Similar Factor-2 (APS-2);7) Sigma Factor Like Factor-1 (SFL-1); and 8) MYB Factor-1 (MYB-1), all from Physcomitrella patens. 
The invention provides in some embodiments that the TFSRP and coding nucleic acid are that found in members of the genus Physcomitrella. In another preferred embodiment, the nucleic acid and protein are from a Physcomitrella patens. The invention provides that the environmental stress can be salinity, drought, temperature, metal, chemical, pathogenic and oxidative stresses, or combinations thereof. In preferred embodiments, the environmental stress can be drought or cold temperature.
The invention further provides a seed produced by a transgenic plant transformed by a TFSRP coding nucleic acid, wherein the plant is true breeding for increased tolerance to environmental stress as compared to a wild type variety of the plant. The invention further provides a seed produced by a transgenic plant expressing a TFSRP, wherein the plant is true breeding for increased tolerance to environmental stress as compared to a wild type variety of the plant.
The invention further provides an agricultural product produced by any of the below-described transgenic plants, plant parts or seeds. The invention further provides an isolated TFSRP as described below. The invention further provides an isolated TFSRP coding nucleic acid, wherein the TFSRP coding nucleic acid codes for a TFSRP as described below.
The invention further provides an isolated recombinant expression vector comprising a TFSRP coding nucleic acid as described below, wherein expression of the vector in a host cell results in increased tolerance to environmental stress as compared to a wild type variety of the host cell. The invention further provides a host cell containing the vector and a plant containing the host cell.
The invention further provides a method of producing a transgenic plant with a TFSRP coding nucleic acid, wherein expression of the nucleic acid in the plant results in increased tolerance to environmental stress as compared to a wild type variety of the plant comprising: (a) transforming a plant cell with an expression vector comprising a TFSRP coding nucleic acid, and (b) generating from the plant cell a transgenic plant with an increased tolerance to environmental stress as compared to a wild type variety of the plant. In preferred embodiments, the TFSRP and TFSRP coding nucleic acid are as described below.
The present invention further provides a method of identifying a novel TFSRP, comprising (a) raising a specific antibody response to a TFSRP, or fragment thereof, as described below; (b) screening putative TFSRP material with the antibody, wherein specific binding of the antibody to the material indicates the presence of a potentially novel TFSRP; and (c) identifying from the bound material a novel TFSRP in comparison to known TFSRP. Alternatively, hybridization with nucleic acid probes as described below can be used to identify novel TFSRP nucleic acids.
The present invention also provides methods of modifying stress tolerance of a plant comprising, modifying the expression of a TFSRP in the plant, wherein the TFSRP is as described below. The invention provides that this method can be performed such that the stress tolerance is either increased or decreased. Preferably, stress tolerance is increased in a plant via increasing expression of a TFSRP.